The invention is based on a device for ascertaining a rate of rotation.
The use of rotation rate sensors, which function for instance on the principle of a vibration gyrometer, in conjunction with systems for regulating the driving dynamics of motor vehicles is already known. Such sensors evaluate the effect of the Coriolis acceleration, which serves as a measure of the actual yaw speed of the vehicle.
Such a rotation rate sensor is described for instance by U.S. Pat. No. 4,759,220. In that patent, the typical construction of such a sensor and the associated evaluation circuit are described in further detail. Essentially, this sensor is a thin-walled hollow cylinder of elastic material. A plurality of piezoelectric sensor elements are mounted on the cylinder wall, with two sensor elements at a time facing one another. These sensor elements are set into constant mechanical drive oscillations with the aid of an oscillator loop. The Coriolis effect, together with a rotary speed coupled in vertically to the drive oscillation, brings about a Coriolis acceleration, which causes a deflection of the drive oscillation in the Coriolis direction. This deflection is a measure for the coupled-in rate of rotation. The resultant output voltage is ascertained with the aid of a detector circuit and finally is utilized to determine the rate of rotation.
The sensor along with the associated evaluation circuit known from U.S. Pat. No. 4,759,220 has the disadvantage that a malfunction cannot readily be detected. If such a sensor is used in conjunction with systems relevant to safety in a motor vehicle, then it is necessary that the operability be monitored.